1. Field of the Invention
The present invention relates to a process for the preparation of 6-aminocaproamide. The 6-aminocaproamide is useful to produce caprolactam, which in turn is useful to produce nylon 6.
2. Description of Related Art
6-Aminocaproamide is a useful intermediate that is suitable for the manufacturing of caprolactam. U.S. Pat. No. 4,119,665 discloses a process for the manufacturing of 6-aminocaproamide by the reaction of ethyl-5-cyanovalerate with ammonia to produce 5-cyanovaleramide, which is then hydrogenated in the presence of ammonia and a supported cobalt and/or nickel catalyst to produce the 6-aminocaproamide. While the process of U.S. Pat. No. 4,199,665 provides good yields of 6-aminocaproamide, it can be hindered by the generation of one mole of ethanol per mole of product. Ethanol handling increases the process costs for waste treatment or recycling. Also, the patent limits the process for the manufacturing of 6-aminocaproamide to the use of a supported cobalt and/or nickel catalyst obtained by a specific process. The catalyst is made by calcining together an appropriate cobalt and/or nickel salt and an Al.sub.2 (OH).sub.16 CO.sub.3 support, thereby forming a solid catalyst which has cobalt and/or nickel distributed throughout it, not just on the surface of the support.
A process for the hydrogenation of cyanocarboxylic acid amides to produce the corresponding aminocarboxylic acid amides in the presence of an unpromoted Raney.RTM. nickel catalyst is described in Chemische Berichte 92,2619 (1959). The reaction of the publication occurs in a dioxane solvent and in the presence of ammonia. A process, which provides a higher rate of reaction and avoids the use of the cancer-suspect agent, dioxane, would be desirable.
A process for the preparation of an aqueous mixture of .epsilon.-caprolactam and .epsilon.-caprolactam precursors, including 6-aminocaproamide is disclosed in published international application WO 9835938. A process that provides a higher yield of 6-aminocaproamide would be desirable from an industrial point of view to simplify purification and provide lower amounts of waste.